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178144
bio website lightandmatter.com
location Fullerton, California
age
visits member for 3 years, 11 months
seen May 21 at 15:35

I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.


Nov
18
comment Is the observable universe growing or shrinking?
In a matter-dominated universe, more objects are always coming inside the horizon, but in a universe dominated by dark energy it's the other way around. Our universe is transitioning from matter-dominated to dark-energy-dominated, so at some point things will stop coming in and start going out, but I think that hasn't happened yet.
Nov
18
revised Are Wormholes predicted by the theory of general relativity?
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Nov
18
revised Are Wormholes predicted by the theory of general relativity?
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Nov
18
revised Are Wormholes predicted by the theory of general relativity?
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Nov
18
answered How to theoretically define a concrete operation to perform in order to measure the length of an object?
Nov
18
revised How to theoretically define a concrete operation to perform in order to measure the length of an object?
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Nov
18
comment No-hair theorems for naked singularities?
@zibadawatimmy: Jerry Schirmer is correct. You're interpreting his statement incorrectly.
Nov
18
comment No-hair theorems for naked singularities?
@zibadawatimmy: I don't think that's right. There are fundamental reasons why subatomic particles can't be GR-style singularities. If electrons were naked singularities, we would have fundamental problems in physics, and we would observe electrons to have very different properties than they actually have.
Nov
18
revised Are Wormholes predicted by the theory of general relativity?
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Nov
18
answered Are Wormholes predicted by the theory of general relativity?
Nov
18
revised No-hair theorems for naked singularities?
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Nov
18
asked No-hair theorems for naked singularities?
Nov
18
revised Do all the spacelike curve terminate at the spatial infinity $i_0$ in the Penrose Diagram of a Schwarzchild black hole?
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Nov
18
comment Is chain reaction possible in stable isotopes?
U235 has a half-life of almost a billion years, so although it's not stable in the absolute sense, it's clearly right on the border, and in the practical sense it's "stable" enough to exist in the earth's crust. It's conceivable, although probably not likely, that there are nuclei in the transuranic island of stability that are stable. If so, then I'm sure they're fissile enough to undergo chain reactions.
Nov
18
comment Do all the spacelike curve terminate at the spatial infinity $i_0$ in the Penrose Diagram of a Schwarzchild black hole?
I would guess that the correct claim is that all spacelike geodesics terminate at $i^0$, in which case your counterexample might fail because it probably isn't a geodesic.
Nov
18
comment Do all the spacelike curve terminate at the spatial infinity $i_0$ in the Penrose Diagram of a Schwarzchild black hole?
Do you really mean all spacelike curves, not all spacelike geodesics, or all spacelike inextensible curves, or all complete spacelike geodesics? If the question is really about all spacelike curves, then there are easy counterexamples, including closed spacelike curves, the spacelike curve from Chicago to LA, and spacelike curves that terminate on the singularity. But all the books state the opposite. What books do you have in mind? Please quote exactly what they claim is true.
Nov
17
comment Does rotation increase mass?
related: physics.stackexchange.com/questions/94921/…
Nov
17
comment $\beta^+$ decay question
[...] out of a Slater determinant of single-particle wavefunctions. It doesn't mean that "there aren't any individual particles." In the final paragraph, the discussion of pp fusion doesn't address the question, which is about beta decay, not fusion reactions that involve a weak-interaction process.
Nov
17
comment $\beta^+$ decay question
The first paragraph is pretty garbled, and it's not clear to me what you have in mind there. It seems as though you think that mass-energy equivalence, along with the fact that nuclear masses aren't equal to $Zm_p+Nm_n$, implies that neutron number and proton number aren't well defined. That's not true. If you have in mind something about the fact that protons and neutrons are composites of quarks, then that isn't coming through clearly here, and in any case isn't relevant. In the second paragraph, I think you're confused about what it means to put a many-body wavefunction together [...]
Nov
17
comment Is the charge distribution for an electric field unique?
Given the field in a region R, are you asking whether (1) the charge density is uniquely determined in R, or (2) whether it's uniquely determined everywhere? If 1, then Valter Moretti's comment answers your question. If 2, then TZDZ's answer.